This invention relates to power line communication systems, and more particularly to a power line communication system that is re-configurable to adapt the utility meter to the specific utility usage and display characteristics of the attached dwelling.
Present utility meter communication devices may employ several electronic parts which result in a high cost of acquisition and maintenance of the communication hardware. It is desirable to have a simple and adaptable utility meter communications system with few parts that can communicate with other utility meters and with a central database using standard protocols.
Currently there are numerous method available for utility meters to communicate to a central location. There are wireless methods, such as those marketed by ITRON(trademark), CELLNET(trademark), and standard protocols that operate in the 900 MHz ISM band. There are methods utilizing Power Line Carrier (PLC) techniques, such as those marketed by INTELLON(trademark). Other methods include the use of integrated telephone modems. Additionally, communication modalities include optical communications, such as industry standard Infrared Data Association (IRDA), or direct communication with an external device via a serial port. In yet another communicating mode, one utility meter may function as a xe2x80x9cbridgexe2x80x9d for communications between other utility meters and a central hub, or to pass information in a daisy-chain manner through meters and eventually to a hub. It is desirable to have a utility meter that can be easily adapted to communicate using a variety of communication methods and protocols.
In electronic utility metering applications, conflicting demands exist for flexibility of metering functions and a low cost electronics metering platform. It is desirable to have a utility meter that uses xe2x80x9csoft-keyxe2x80x9d to select measurement, calibration, and display features of the utility meter.
While LCD (Liquid Crystal Display) driver integrated circuits are readily available from many commercial sources, they are costly for high volume applications which have simple display requirements, such as electric meters. Typical LCD driver implementations use analog circuits to develop the multiple voltage levels required to drive multiplexed LCDs. Some implementations use voltage references and voltage multipliers to produce the required voltages which are coupled onto the LCD driver lines as required. Other drivers use resistive dividers to produce voltages necessary to drive the LCD segments. Resistive dividers require external parts and consume additional power. It is desirable to have a low cost and low power LCD driver which utilizes a microprocessor to drive the LCD display.
High volume electric meters, such as residential electric meters, are typically designed with cost economy as a primary goalxe2x80x94a large contributor to the cost of such a meter is the power supply. Thus, it is important to design the meter optimizing the cost of the power supply. When power is removed from the typical utility meter it is important that the meter power supply contain enough stored energy to allow the meter to continue to function for a short time (i.e., ≈100 ms) so as to store important information, such as accumulated kilowatt-hours, in non-volatile memory. The alternative is to simply lose all information stored in volatile memory when power is lost. Providing an appropriate power-off sequence for the meter can reduce the energy requirement of the power supply, saving cost in the meter while still allowing important information to be saved.
In a typical solid state electric meter many functions of the meter such as metering algorithms, time-keeping, display, communications, etc., are controlled by a central processor. Each of these functions has a varying degree of importance in the event of a power failure. It is desirable to have a utility meter with an appropriately sized power supply to enable the utility meter to recover from a loss of power in a predictable manner.
In cost sensitive applications such as residential electricity meters, typical assembly techniques which include wires and soldered electrical connectors add unnecessary cost to the electric meter. A typical assembly technique includes soldering to the voltage bus-bar wires with relatively expensive connectors which are then attached to the printed wiring board (PWB) during assembly. It is desirable to have a utility meter that can be quickly and easy assembled without the use of soldered connections, screws, and wire bundles.
Traditionally, an iterative approach has been used in the calibration of residential electromechanical and electronic electricity meters, requiring a high accuracy meter standard, a single-bit test output signal, and multiple calibration cycles or multiple calibration stations under various test conditions. Traditionally, the test setup uses fixed currents at 3 Amps, and 30 Amps for these calibration points as required by the utility industry. These procedures require a count of the number of transitions of the single-bit test output signal over a fixed period of time to calibration the meter. It is desirable to employ a utility meter that can be quickly calibrated and accurately calibrated without having to count the number of transitions of a single-bit output signal.
The present invention addresses the foregoing needs by providing a power line communications system that is built to be modular so as to be re-configurable through the use of hardwire re-configurable jumper wires or soft-keys. Reconfiguration of the power line communications system is based on factors including: harmonic content of the power signal measured, the selection of an alternative electronic display, communication protocols with external devices, whether to provide time of use measurements, band-pass filter settings, low-pass filter settings, high-pass filter settings, and power quality measurements.
In a further exemplary embodiment a digital integrator is employed which integrates alternating current signals while at the same time is insensitive to residual direct current sub-components of the alternating current signals within the electronic utility meter.
In a further exemplary embodiment a liquid crystal display (LCD) driver is employed in the electronic utility meter which utilizes a capacitor multiplexer, wherein an array of multi-level voltage signals are generated by arranging a plurality of capacitors, having preselected capacitance values, and being coupled to a multiplexer, so as to drive the LCD with the multi-level voltage signals.
In a further exemplary embodiment a method of powering down the electronic utility meter is employed which selectively removes power from functions within the meter and stores critical operating parameters in non-volatile memory based on respective voltage levels of a monitored internal power supply signal.
In a further exemplary embodiment a method of calibrating the electronic utility meter to obtain optimal utility usage measurements is employed where utility usage measurements are made at the user site and adjustments are made on-the-fly to compensate for electronic utility meter sensor variability, circuitry variability, and user site usage data variability.
In a further exemplary embodiment components are employed to reduce the amount of soldering and assembly time of the current sensors employed in the electronic utility meter. A printed wiring board and a plurality of connectors are employed which cooperate to eliminate the need to solder wires to the base and printed wiring board. All components are selected so that each respective component may fit into pin connectors and socket connectors which are, in turn, mechanically snapped to the printed wiring board. Snap together housings are employed which eliminate the need for screws, bolts, and glue to hold sub-components to the printed wiring board, and which hold the housings together. Finally, current sensors are employed which are in electrical communication with the printed wiring board without the use of soldering, screws, and bolts, and which are secured to the housings without the use of solder screws and bolt.